The present invention relates to communications systems, and more particularly, to the transfer of data regarding geographic positions of mobile terminals and mobile terminal users in wireless communications systems.
Wireless communications systems are pervasive in the world today. For example, a significant percentage of individuals in developed nations already personally own at least one cellular telephone for use with well established land-based and satellite-based systems. Furthermore, a growing number of developing nations are now bringing wireless systems on line. This insatiable global appetite for wireless technology will only intensify in the foreseeable future.
FIG. 1 depicts an exemplary wireless communications system 100 including ten cells or coverage areas C1-C10, ten base stations B1-B10, a Mobile Switching Center MSC and ten mobile stations M1-M10. Such a wireless system 100 can be constructed, for example, in accordance with any of the well known wireless communications standards, including the European Global System for Mobile (GSM) cellular standard or the United States Digital Cellular (USDC) standard (i.e., the Electronic Industry Association Interim Standard IS-54). While such a system 100 typically includes far more than ten cells, ten base stations and ten mobile stations, ten of each component is sufficient for illustrative purposes.
As shown, one or more base stations can be situated in each of the cells. Although FIG. 1 shows the base stations located toward the cell centers, each base station can instead be located anywhere within a cell. Base stations located toward a cell center typically employ omni-directional antennas, whereas base stations located toward a cell boundary typically employ directional antennas. Those skilled in the art will also appreciate that each individual base station shown in FIG. 1 can, in practice, comprise a base station controller in communication with a number of separate base station units, each unit providing coverage for a cell sector.
Typically, each base station and each mobile station includes a radio transceiver for transmitting and receiving communications signals over the air interface (as defined, for example, by one of the known standards, GSM, IS-54, etc.). More specifically, the base and mobile stations communicate using a form of time, frequency or code division multiple access (i.e., TDMA, FDMA or CDMA) as is known in the art. As the mobile stations move within a cell and from cell to cell, communication with at least one base station is always possible. As a result, mobile station users are able to place, receive and conduct calls from anywhere within the overall system coverage area.
As shown, the base stations are also in communication with the MSC. Though only one MSC is shown in FIG. 1, those of skill in the art will appreciate that an overall system typically includes multiple MSCs, each MSC being coupled (e.g., by radio or hard-wire link) to a unique subset of the base stations in the overall system, and each MSC being capable of communicating with the other MSCs in the system (e.g., via the U.S. Signaling System No. 7, or SS7, protocol). As is known in the art, the MSCs keep track of which cells the mobile stations are registered in and provide a link between the wireless system 100 and the Public Switched Telephone Network (PSTN).
To keep track of which cells the mobile stations are registered in, each MSC typically maintains a Visiting Location Register (VLR) which provides a list of mobile stations presently registered within the coverage area of the MSC (i.e., in the coverage area serviced by all of the base stations which are coupled to the MSC). Furthermore, at least one Home Location Register (HLR) is typically maintained for an overall system, the HLR conventionally providing a list of all local subscribers based within the system coverage area and also providing, for each local subscriber, a description of the various features available to the subscriber. When a mobile station moves into a new coverage area and registers with a new MSC (via a coupled base station), the visited MSC updates its VLR to reflect the presence of the mobile station and also contacts the HLR to obtain subscription information for the mobile station. In this way, mobile stations can seamlessly roam from coverage area to coverage area while maintaining the ability to place and receive calls in accordance with their base subscription.
Conventionally, there has been a strong connection between a wireless subscription and a particular mobile terminal and a particular mobile user. In other words, an individual user conventionally purchases a subscription with which a particular terminal is associated (e.g., by Mobile Identification Number, or MIN), and the individual user is charged for calls placed from the particular terminal. Additionally, calls are conventionally placed by dialing a number associated with a particular terminal, and thus varying numbers are used to reach an individual, depending upon which of many terminals the individual happens to be near.
More recently, however, the growing demand for wireless technology has required a more sophisticated approach to system management. In particular, there has been a recent push toward a global system in which calls are made, not from terminal to terminal, but from user to user. In other words, a system in which each user has a unique identification number by which all calls to that user are placed, irrespective of which terminal the user happens to be using. Toward that end, the concepts of user, terminal and subscription are beginning to diverge. See, for example, co-pending U.S. patent application Ser. No. 08/585,149, filed Jan. 10, 1996 and entitled Cellular Telecommunication Systems having Selectively Associatable Usage Parameters, which is incorporated herein by reference. Consequently, the above described Home and Visiting Location Registers can now include distinct user, terminal and subscription databases.
Recently (e.g., with the advent of the Global Positioning System, or GPS), there has also been a push toward enabling a wireless communications system to provide detailed information regarding the geographic position of users and terminals. However, while the MSCs in a conventional wireless system can determine the cell in which a mobile terminal is located, they typically cannot provide the more precise location information which is often necessary or desirable in practice (e.g., when an individual must be located in an emergency situation or when system operations personnel wish to locate a particular terminal for maintenance or repair). Further, known methods for providing more precise location information (see, e.g., U.S. Pat. No. 5,727,057 to Emery et al.) do not account for the recent divergence of the concepts of user, terminal and subscription.
Consequently, there is a need for improved techniques for ascertaining the geographic location of a mobile terminal in a wireless communications system.
The present invention fulfills the above-described and other needs by providing methods and apparatus for ascertaining the geographic position of users and terminals in a wireless communications system. Embodiments of the invention enable system users to easily request the position of a terminal (e.g., when operations personnel wish to locate a terminal in order to perform maintenance of traffic system performance or to determine the reasons for lost calls) or the position of a user (e.g., when emergency personnel wish to locate a lost or injured individual). Further, embodiments of the invention permit mobile terminals to be used as navigation instruments and open the door to more sophisticated supervision of taxis, buses and other transport vehicles. Advantageously, aspects of the invention can be readily incorporated within a wireless communications protocol which contemplates the distinct concepts of user, terminal and subscription.
An exemplary method for requesting and obtaining user position information in a wireless communications system includes the steps of: sending terminal position information from user terminals to mobile switching centers with which the user terminals are registered; storing the terminal position information in visiting location registers of the receiving mobile switching centers; entering a feature code and a user identification code at a requesting terminal (the feature code and user identification code indicating a request for position information regarding a remote system user associated with the user identification code); sending a user position request message and the user identification code from the requesting terminal to a mobile switching center with which the requesting terminal is registered; forwarding the user position request message from the mobile switching center to a home location register in the system; determining (at the home location register) which user terminals the remote system user is registered with; sending a terminal position request message and the user identification code to each mobile switching center where the remote user is registered on a terminal; retrieving (for each terminal with which the remote user is registered) terminal position information from a visiting location register; sending (for each terminal with which the remote user is registered) a terminal position request acknowledged message, a terminal identification code and retrieved terminal position information to the home location register; and forwarding at least one of the terminal position request acknowledged messages from the home location register to the requesting terminal.
Prior to determining which user terminals the remote system user is registered with, a determination can be made (e.g., at the home location register) whether position information requests for the remote user are barred. If so, a user position request not acknowledged message can be sent from the home location register to the mobile switching center with which the requesting terminal is registered, and then back to the requesting terminal.
According to exemplary embodiments, a user terminal can include a global positioning system receiver for determining position coordinates. Alternatively, the user terminal can compute position coordinates based on at least one timing advance parameter received from at least one base station in the wireless communications system. In either case, the user terminal can periodically transmit position coordinates to a mobile switching center with which it is registered. Alternatively, the mobile switching center can periodically poll the user terminal for position coordinates, or wait and request the position coordinates when a request for position information regarding the user terminal is made.
An exemplary wireless communications system according to the invention includes a plurality of user terminals, at least one mobile switching center (each mobile switching center including a visiting location register), and at least one home location register. According to exemplary embodiments, each user terminal is configured to transmit terminal position information to a mobile switching center with which the user terminal is registered, and each mobile switching center is configured to store received terminal position information in a corresponding visiting location register. Additionally, the home location register is configured to receive requests for position information relating to target users registered in the system and, for each received request, to send a terminal position request to each mobile switching center where a target user is registered on a terminal. Upon receiving terminal position requests, the mobile switching centers can retrieve terminal position information from their visiting location registers and transmit the retrieved terminal position information to the home location register.
The above-described and other features and advantages of the invention are explained in detail hereinafter with reference to the illustrative examples shown in the accompanying drawings. Those of skill in the art will appreciate that the described embodiments are provided for purposes of illustration and understanding and that numerous equivalent embodiments are contemplated herein.